Braking force control apparatus for vehicle

Abstract

A braking force control apparatus is provided which has a first system including a first upstream braking actuator and a first downstream braking actuator, a second system including a second upstream braking actuator and a second downstream braking actuator, and a control unit. When the downstream braking actuator is abnormal and the upstream pressure can be supplied to braking force generating devices, but a braking pressure of any one of the wheels cannot be normally controlled, the control unit select the pressure increasing side control mode out of the front wheel control modes as a first prescribed control mode, select the pressure decreasing side control mode out of the rear wheel control modes as a second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes.

What is claimed is: 
     
         1 . A braking force control apparatus for a vehicle which has a first system for controlling braking forces of left and right front wheels, a second system for controlling braking forces of left and right rear wheels, and a control unit for controlling the first and second systems; the first system includes a first upstream braking actuator including a master cylinder device and generating a first upstream pressure common to the left and right front wheels, and a first downstream braking actuator that individually controls braking pressures supplied to braking force generating devices of the left and right front wheels using the first upstream pressure; and the second system includes a second upstream braking actuator including the master cylinder device and generating a second upstream pressure common to the left and right rear wheels and a second downstream braking actuator that individually controls braking pressures supplied to braking force generating devices of the left and right rear wheels using the second upstream pressure,
 the control unit is configured to, when an anti-skid control starting condition is satisfied for any one of the wheels, control the first or second downstream braking actuator for the relevant wheel in control modes of a pressure increasing mode, a pressure holding mode and a pressure decreasing mode so that a degree of braking slip of the relevant wheel falls within a predetermined range until an anti-skid control ending condition is satisfied, and control the first and second downstream braking actuators in a non-control mode so that braking pressures of the wheels other than the relevant wheel become values corresponding to a braking operation amount of a driver, wherein   the first and second upstream braking actuators are configured to control the first and second upstream pressures, respectively, in control modes of a pressure increasing mode, a pressure holding mode, a pressure decreasing mode and a non-control mode, and set the first and second upstream pressures to a pressure in the master cylinder device when the control mode is the non-control mode, and   the control unit is configured, in selecting the control mode on a pressure increasing side, a priority of selection being set higher in the order of the pressure increasing mode, the pressure holding mode, the pressure decreasing mode and the non-control mode, and in selecting the control mode on a pressure decreasing side, the priority of selection being set higher in the order of the pressure decreasing mode, the pressure holding mode, the pressure increasing mode, and the non-control mode, to select a pressure increasing side control mode out of the control modes of the left and right front wheels as a first prescribed control mode, to select a pressure decreasing side mode out of the control modes of the left and right rear wheels as a second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a specific abnormality in which the first and second upstream pressures can be supplied from the first and second upstream braking actuators, respectively, to the braking force generating devices of the corresponding wheels but a braking pressure supplied to the braking force generating device of any one of the wheels cannot be reduced occurs in the first and/or second downstream braking actuators.   
     
     
         2 . The braking force control apparatus for a vehicle according to  claim 1 , wherein the control unit is configured to select the pressure decreasing side mode out of the control modes of the left and right front wheels as the first prescribed control mode, to select the pressure decreasing side mode out of the control modes of the left and right rear wheels as the second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a running state of the vehicle is unstable. 
     
     
         3 . The braking force control apparatus for a vehicle according to  claim 1 , wherein the control unit is configured to select the pressure increasing side control mode out of the control modes of the left and right front wheels as the first prescribed control mode, to select the pressure increasing side control mode out of the control modes of the left and right rear wheels as the second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a running state of the vehicle is stable and the vehicle is not turning. 
     
     
         4 . The braking force control apparatus for a vehicle according to  claim 1 , wherein the control unit is configured to select the pressure increasing side control mode out of the control modes of the left and right front wheels as the first prescribed control mode, to select the pressure decreasing side control mode out of the control modes of the left and right rear wheels as the second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a running state of the vehicle is stable and the vehicle is turning. 
     
     
         5 . A braking force control apparatus for a vehicle which has a first system for controlling braking forces of left front wheel and right rear wheel, a second system for controlling braking forces of right front wheel and left rear wheel, and a control unit for controlling the first and second systems; the first system includes a first upstream braking actuator including a master cylinder device and generating a first upstream pressure common to the left front wheel and the right rear wheel, and a first downstream braking actuator that individually controls braking pressures supplied to braking force generating devices of the left front wheel and the right rear wheel using the first upstream pressure; and the second system includes a second upstream braking actuator including the master cylinder device and generating a second upstream pressure common to the right front wheel and the left rear wheel and a second downstream braking actuator that individually controls braking pressures supplied to braking force generating devices of the right front wheel and the left rear wheel using the second upstream pressure,
 the control unit is configured to, when an anti-skid control start condition is satisfied for any one of the wheels, control the first or second downstream braking actuator for the relevant wheel in control mode of a pressure increasing mode, a pressure holding mode and a pressure decreasing mode so that a degree of braking slip of the relevant wheel falls within a predetermined range until an anti-skid control ending condition is satisfied, and control the first and second downstream braking actuators in a non-control mode so that braking pressures of the wheels other than the relevant wheel become values corresponding to a braking operation amount of a driver, wherein   the first and second upstream braking actuators are configured to control the first and second upstream pressures, respectively, in control modes of a pressure increasing mode, a pressure holding mode, a pressure decreasing mode and a non-control mode, and set the first and second upstream pressures to a pressure in the master cylinder device when the control mode is the non-control mode, and   the control unit is configured, in selecting the control mode on a pressure increasing side, a priority of selection being set higher in the order of the pressure increasing mode, the pressure holding mode, the pressure decreasing mode and the non-control mode, and in selecting the control mode on a pressure decreasing side, the priority of selection being set higher in the order of the pressure decreasing mode, the pressure holding mode, the pressure increasing mode, and the non-control mode, to select a pressure decreasing side control mode out of the control modes of the two wheels of the first system as a first prescribed control mode, to select a pressure decreasing side mode out of the control modes of the two wheels of the second system as a second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a specific abnormality in which the first and second upstream pressures can be supplied from the first and second upstream braking actuators, respectively, to the braking force generating devices of the corresponding wheels but a braking pressure supplied to the braking force generating device of any one of the wheels cannot be reduced occurs in the first and/or second downstream braking actuators.   
     
     
         6 . The braking force control apparatus for a vehicle according to  claim 5 , wherein the control unit is configured to select the pressure increasing side control mode out of the control modes of the two wheels of the first system as the first prescribed control mode, to select the pressure increasing side control mode out of the control modes of the two wheels of the second system as the second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a running state of the vehicle is stable and the control modes of the left and right rear wheels are not the pressure decreasing mode. 
     
     
         7 . The braking force control apparatus for a vehicle according to  claim 5 , wherein the control unit is configured to select the pressure decreasing side control mode out of the control modes of the two wheels of the first system as the first prescribed control mode, to select the pressure decreasing side control mode out of the control modes of the two wheels of the second system as the second prescribed control mode, and to control the first and second upstream pressures in the first and second prescribed control modes, respectively when a running state of the vehicle is stable but at least one of the control modes of the left and right rear wheels is the pressure decreasing mode.